FR2634196A1 - PROCESS FOR THE PREPARATION OF METHOXYACETIC ACID - Google Patents

Abstract

The present invention relates to a process for preparing methoxyacetic acid from monochloroacetic acid, sodium methoxide and methanol. This process is characterized in that it consists in reacting monochloroacetic acid and sodium methoxide, employed in a molar ratio of 0.5 / 1.1 to 1.2, optionally in the presence of a solvent consisting of methanol containing methyl ester of methoxyacetic acid, at elevated temperature, preferably at the boiling point of the reaction mixture, to separate the methanol by distillation and, after addition of the methyl ester of methoxyacetic acid, to react the mixture, with stirring, with dry hydrochloric acid gas then to eliminate the sodium chloride which forms, to separate by distillation the methyl ester of methoxyacetic acid and to proceed with the purification of the methoxyacetic acid obtained, if necessary by vacuum distillation.

Description

The subject of the present invention is a new preparation process

  of methoxyacetic acid. Methoxyacetic acid is a chemical intermediate of great importance. Firstly it is the basic material for methoxyacetylation, ie methoxyacetyl chloride is prepared from methoxyacetic acid, and it is widely used in the pharmaceutical industry and the production of plant protection agents. In addition this compound can also be used as a plasticizer and dye. It is also used as an auxiliary

  in the textile industry than in flotation techniques.

  Various methods of preparing methoxyacetic acid are known. Among these processes are the following which use monochloroacetic acid and their salts as well as methanol: USP 2,450,741 (1949) discloses a process in which monochloroacetic acid and methanol are boiled in an autoclave for four hours at 200 ° C. until a mixture of methoxyacetic acid, methyl chloride and dimethyl ether is obtained. The acid yield

methoxyacetic is 35%.

  According to DE-PS-2 759 169 (1979) sodium monochloroacetate, methanol and sodium methoxide are boiled for two hours at 75 ° C. and the mixture obtained is then evaporated to dryness. The residue is dissolved in rendered water

  acid by adding hydrochloric acid and then the water is removed.

  distilled. Then add to the reaction mixture

  toluene and the residual water and excess hydrochloric acid are removed by distillation. The sodium chloride is then filtered hot and then washed with toluene. The toluene solutions are combined and fractionated by distillation. After distilling toluene, the methoxyacetic acid is purified by distillation under

  empty. The yield obtained is 85%.

  The disadvantages of these processes are as follows: the starting material is sodium monochloroacetate which must be prepared in a separate operation; after completion of the reaction the excess of methanol must be separated by distillation, it is necessary to add water to the sodium methoxide, to acidify by addition

  hydrochloric acid and then distil the water

  tion. By acidifying the methanol, sodium methoxide is formed and in a reaction medium containing hydrochloric acid, this leads to the formation of an ester with methoxyacetic acid. This compound must be separated from water, hydrochloric acid and methoxyacetic acid; at the same time that water separates by distillation from

  methoxyacetic acid, which is difficult to

  -operate; - the fact that one operates in aqueous solution is always present in the system of sodium chloride in the state

  dissolved substances whose tank separation causes problems

my during the distillation.

  The subject of the present invention is a simple and inexpensive method of using as starting material monochloroacetic acid, which method furthermore has the advantage of avoiding the formation of secondary products and

  allow the reagents to be recycled to the synthesis zone.

  The process according to the present invention for the preparation of methoxyzetic acid from monochloroacetic acid, sodium methoxide and methanol is characterized in that it consists in reacting monochloroacetic acid and sodium methoxide, employed in one molar ratio of 0.5 / 1.1 to 1.2, optionally in the presence of a methanol solvent containing methoxyacetic acid methyl ester,

  at elevated temperature, preferably at the boiling point

  the reaction mixture, to be distilled off

  methanol and, after addition of methylester of methoxy-

  acetic acid, to react the mixture, with stirring, with dry gaseous hydrochloric acid and then to remove the chloride

  of sodium which is formed, to distill off the methyl-

  methoxyacetic acid ester and to carry out the purification

  cation of the methoxyacetic acid obtained, where appropriate by vacuum distillation. The reaction of hydrochloric acid and the sodium salt of methoxyacetic acid, also known as sodium methoxyacetate, present in the anhydrous methoxyacetic acid methyl ester medium is carried out at a temperature of 50.degree. between 20 and C. The precipitated sodium chloride is removed by filtration and washed with methanol. The methanol used for the washing may contain methoxyacetic acid and the methyl ester of methoxyacetic acid. The methylester of methoxyacetic acid is removed by distillation (it may optionally contain free acid), and is recycled to

  the synthesis zone where it acts as a solvent.

  According to the process of the present invention the monohydric acid

  chloroacetic acid is dissolved in methanol or methyl ester

  methoxyacetic acid. This methyl ester of methoxy

  acetic acid so used is not necessarily a product

  pure; it may contain monochloroacetic acid, methacrylate

  methoxyacetic acid, because these compounds enter into

  play during the reaction. Compared to the stoical conditions

  the chiometrials of the reaction, an excess of sodium methoxide is used. When the reaction of the monochloroacetic acid is complete, the methanol is distilled off and is acidified by addition of dry gaseous hydrochloric acid. The precipitated sodium chloride is filtered off and washed with methanol which is recycled to the reaction. The

  Methyl ester of methoxyacetic acid is distilled off

  lation and is also recycled to the synthesis zone. The residue obtained is methoxyacetic acid having a purity of 95 to 98%; he may undergo further purification

by vacuum distillation.

  The advantages of the process according to the present invention as compared with the known processes are summarized below: 1) monochloroacetic acid is used directly in

  as a starting point and the preparation of the mono-

  Sodium chloroacetate in a separate step is avoided. 2) according to this process, methoxyacetic acid is obtained

  at a yield of 90% compared with monochloroacetic acid

  starting roacetic; 3) the possibility of the formation of glycolic acid is excluded since it operates in an anhydrous medium;

  (4) the resulting product does not contain any impurities

  as monochloroacetic acid because of the use of

  If the sodium methoxide is in excess of the stoichiometric amount, the reaction can be complete. ) the required apparatus is much simpler than in the known methods. It is not necessary to use an apparatus capable of withstanding the pressure as is the case by operating according to the method of

  US Patent 2,458,741. Dilution in water, acidification

  cation, the distillation of water as well as the extraction using a solvent which are necessary if one operates

  according to the method of DE-PS-2 759 169 are not nec-

  when operating according to the process of the present invention. In addition, the possibility of salt precipitation is avoided which inevitably occurs during the distillation used in the methods used.

work in an aqueous medium.

  6) the methoxyacetic acid is present in the solvent during the whole of the synthesis and it is not obtained

  by extraction; only the solvent is distilled off

  the resulting product is small.

  7) using the method according to the present invention

  It is possible to protect the environment because

  They do not come into contact with water so that the formation of aqueous effluents is avoided. After washing with methanol the sodium chloride thus prepared

  has a purity greater than 99% and may be directly

  used in industrial applications. The distillatively separated methanol has a purity greater than 99% so that it can be used in a separate distillation step. By combustion of the residue of the vacuum distillation vessel only carbon dioxide and water are formed.

  who have no action on the environment.

  8) in the synthesis made from monochlorinated

  In acetic acid, sodium salt is generally used as the starting material and is reacted with sodium methoxide. In this way a single preparation step is necessary because the sodium monochloroacetate must be prepared in a separate step which leads to some losses. If chloroacetic acid is used directly as a starting material, which is the case by operating according to the method of US-PS-2 450 741, then a non-uniform product is formed.

  and an extremely low yield (35%) is obtained.

  9) the aforementioned disadvantages are eliminated by the method according to the present invention. Monochloroacetic acid is used as a starting material, which consequently avoids the preparation of the sodium salt and makes it possible to obtain a better yield (90% relative to

  starting monochloroacetic acid).

  According to DE-PS 2 759 169, the acidification is carried out in an aqueous medium in the presence of concentrated hydrochloric acid. This is a real disadvantage because methoxyacetic acid is very difficult to separate from the aqueous medium. Also, in the process of the present invention is an anhydrous medium used?

  during acidification. As, however, in treating metha-

  If the methoxyacetic acid methylester is formed by hydrochloric acid in an anhydrous medium, the methanol should be removed before acidification. As a solvent,

  will preferably be used in the reaction with chloroacid

  methoxyacetic acid methylester because it dissolves the various compounds present in the reaction relatively satisfactorily and can be separated from the methoxyacetic acid by distillation due to its boiling point which is at a temperature of 70 ° C. lower than

that of methoxyacetic acid.

Example 1

  47.25 g (0.5 moles) of monochloroacetic acid are dissolved in 200 cm3 of methoxyacetic acid methyl ester and the methanolic solution comprising 200 g of sodium methoxide (1.1 mole) at 30% is added dropwise to drop, at 40 C and with good stirring. In a distillation column the methanol starts to slowly separate by distillation while 50 cm3 of wash methanol from a previous production step is added. All methanol

  added must be removed from the system during distillation.

  At the end of this distillation, the temperature in the tank at least reaches 100 C. The reaction medium is then cooled.

  and during this cooling, the methoxy acid is recovered.

  acetic acid of its sodium salt by operating at 25-30 C in the presence of dry gaseous hydrochloric acid. The precipitated sodium chloride is separated by filtration. 50 to 100 cm3 of methanol are washed (this washing methanol being used in

  subsequent distillation). Methyl ether of methoxy acid

  The acetic acid used as the solvent is separated from the filtrate by distillation under a pressure of the order of 40 bar. The

  resulting crude product contains 95 to 98% methoxy

  acetic acid and can be purified by vacuum distillation.

  Thus, 40.5 g of methoxyacetic acid are obtained, which

  corresponds to a yield of 90% compared to the mono-

  starting chloroacetic acid. The product obtained has a purity of at least 99%. The total amount of glycolic acid

  and monochloroacetic acid present is less than 0.2%.

Example 2

  47.25 g (0.5 mol) of monochloroacetic acid are dissolved in 100 cm3 of molyol and, with good stirring, 200 g of sodium methoxide (1.1 mole) at 30%, dropwise, are added dropwise. at 40 C. The reaction mixture is then brought to boiling. The mixture is analyzed and if the reaction is not complete and the monochloroacetic acid can still be

  present in the reaction mixture, a quantity of

  added sodium methoxide and carry the mixture

  reaction to a new boil until completely eliminated.

chloroacetic acid.

  Then a separating column is placed above the tank and the methanol is separated by distillation. At the same time washing methanol from the previous step used for the washing of sodium chloride is also added. The distillation continues until complete elimination of the methanol. The temperature of the tank is then raised to at least 100 ° C. 200 cm 3 of methyl ester of methoxyacetic acid are then added to the residue and the reaction mixture formed is

  cooled. Under cooling, the hydrochloric acid is introduced.

  than gaseous dry at 25 C until the methoxyacetic acid is completely free of any trace of sodium methoxyacetate. The precipitated sodium chloride is filtered and washed with 50 cm3 of methanol (this washing methanol is used for the distillation of methanol in the subsequent production step). The methyl ester of methoxyacetic acid used as the solvent is then separated by distillation under a pressure of 40 bar. The residual crude product has a purity of 95% and is subjected to purification by vacuum distillation. The yield is 90 to 91% relative to the monochloroacetic acid, the amount of impurities in the product

being less than 0.2%.

Claims (5)

  1. A process for preparing methoxyacetic acid from monochloroacetic acid, sodium methoxide and methanol is characterized in that it consists in reacting the monochloroacetic acid and the sodium methoxide, employed in a molar ratio from 0.5 / 1.1 to 1.2, optionally in the presence of a methanol solvent containing methoxyacetic acid methylester, at elevated temperature,   preferably at the boiling temperature of the reaction mixture   the distillation of methanol and, after addition of methylester of methoxyacetic acid,   react the mixture, with stirring, with hydrochloric acid   dry gas gaseous then remove the sodium chloride that is formed, distill methyloxy ester methoxyacetic acid and proceed to the purification of the resulting methoxyacetic acid, if necessary by vacuum distillation.   2. A process as claimed in the claim   1, which consists in carrying out the reaction between the sodium salt of methoxyacetic acid present in the medium containing anhydrous methoxyacetic acid, and the gaseous hydrochloric acid at a temperature of between 20 and C.   3.- A process as claimed in the claim   1, which consists in separating the chloride of   precipitated sodium and wash it with methanol.   4. A process as claimed in the claim   3, which consists in using, for washing, methanol containing methoxyacetic acid and methylester of methoxyacetic acid.   5.- A process as claimed in the claim   1, which comprises recycling the methylester of the filtered methoxyacetic acid, which may contain free acid, to the synthesis step where it acts as a solvent.